#include <cstdio>
#include <vector>

using namespace std;

vector <int> v;//,q,w;
int n,e,prec,m,s;

void citire()
{
    freopen("oo.in","r",stdin);
    scanf("%d", &n);
    int w;
    for (int i=1; i<=n; i++)
    {
        scanf("%d", &w);
        v.push_back(w);
    }
}

void Oo()
{
    m=0;
    prec=-99;
    for (int i=1; i<n-2; i++)
    {
        //q.push_back(v[i]+v[i-1]);
        //w.push_back(0);
        if (i-prec>=3)
        {
            m+=v[i]+v[i-1];
            prec=i;
          //  w[i]=1;
            e=v[i]+v[i-1];
        }
        else if (e<v[i]+v[i-1])
        {
            m-=e;
            m+=v[i]+v[i-1];
            //w[prec]=0;
            //w[i]=1;
            prec=i;
            e=v[i]+v[i-1];
        }
    }
    freopen("oo.out","w",stdout);
    printf("%d\n", m);
    //q.push_back(v[0]+v[n-1]);
    //w.push_back(0);

}

int main()
{
    citire();
    Oo();
    return 0;
}